Digital Subscriber Line (DSL) technology allows subscribers to transmit both data and voice signals over the same twisted-pair copper telephone line. Data is transmitted over the line by signals using a communication frequency spectrum. Various DSL protocols, referred to in combination as XDSL, may manage the communication spectrum differently. The Synchronous Digital Subscriber Line (SDSL) protocol allows equal portions of the spectrum to be used to transmit data to and receive data from a subscriber. The Asynchronous Digital Subscriber Line (ADSL) protocol allows a larger part of the spectrum to be used to transmit data to a subscriber.
DSL connections use typical copper lines in telephone networks, and multiple copper wires are bundled together into cables called “binder groups.” Electrical energy transmitted across one twisted-pair line may radiate energy onto adjacent twisted-pair lines, causing “crosstalk” or spectral interference on the adjacent lines. Different DSL protocols may be susceptible to different forms of crosstalk. For example, the ADSL protocol may be limited by far-end crosstalk, while the SDSL protocol may be more limited by near-end crosstalk.
Many DSL subscribers may be connected to a single central office using one or more digital subscriber line access multiplexers (DSLAM). Each DSLAM couples many DSL connections to a high-speed backbone network, such as an Asynchronous Transfer Mode (ATM) network. This allows multiple DSL users to access the backbone network at the same time.
The use of a DSLAM to connect multiple subscribers to the same backbone network may cause problems if different subscribers want to receive DSL service using different protocols. It is often difficult to configure a communication system to optimally support one DSL protocol without detrimentally impairing service using another DSL protocol. One approach involves the use of signal power limitations, which limit the amplitude, frequency distribution, and total power of electrical signals transmitted by a DSL carrier. Each DSL protocol has a corresponding signal power limitation. A DSL connection using a particular protocol cannot exceed that protocol's signal power limitation.
A problem with this approach is that power limitations may prevent some potential customers from receiving DSL service. Some potential customers may not be located near a central office. In order for a potential customer to receive DSL service using a particular protocol, a DSL carrier may need to use a signal power that exceeds the power limitations for that protocol. The potential customer may not be able to receive the type of DSL service that the customer wants.
Another problem with this approach is that the signal power limitations may prevent carriers from optimally using each DSL protocol. A carrier may be prevented from using a DSL protocol at an optimal level by the signal power limitations, even though the carrier would not be interfering with other DSL services at that time.
Further, it is difficult to ensure that all carriers are complying with the signal power guidelines. One carrier providing service through a central office cannot ensure that other carriers using the same central office are complying with the signal power limitations. A carrier that fails to comply with the limitations may detrimentally interfere with other carriers with little or no risk of detection.